masakit ang pempem

base on calculation of my last period sept.9 will be my due date. but base on my ultrasound which doesnt need to know my last menstrual says that august 27 will be my due date.. now on my 35 or 37 weeks pregnancy i suddenly suffered pain on my vagina and around of it.. what could be the reason why i suffering this kind of pain?? TIA 😊